Durham climate

Durham Frost Dates and Growing Season

NOAA 1991-2020 normals for Chico Univ Farm, 5.3 km from Durham, elevation 185 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Chico Univ Farm. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around March 4 and the first fall freeze around November 17, a growing season of about 257 days.

Median at 36°F
last April 5, first November 4
Median at 32°F
last March 4, first November 17
Median at 28°F
last February 5, first December 3

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FApr 21Apr 16Apr 11Apr 8Apr 5Apr 1Mar 27Mar 20Mar 13
32°FApr 2Mar 23Mar 15Mar 8Mar 4Feb 28Feb 24Feb 19Feb 8
28°FMar 1Feb 23Feb 18Feb 11Feb 5Jan 31Jan 22Jan 14Jan 1
24°FFeb 3Jan 28Jan 21Jan 14Jan 9Jan 2Dec 31Dec 23Dec 11
20°FJan 23Jan 14Jan 6Jan 2Dec 31Dec 29Dec 21Dec 13Dec 7
16°F–––––––––

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 21Oct 26Oct 31Nov 1Nov 4Nov 7Nov 9Nov 14Nov 19
32°FNov 1Nov 6Nov 10Nov 14Nov 17Nov 21Nov 24Nov 28Dec 5
28°FNov 13Nov 21Nov 26Nov 30Dec 3Dec 7Dec 14Dec 23Jan 5
24°FNov 28Dec 3Dec 9Dec 15Dec 22Dec 28Jan 1Jan 8Jan 18
20°FDec 3Dec 8Dec 14Dec 21Dec 28Dec 31Jan 3Jan 9Jan 22
16°F–––––––––

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F239231225219214209204199190
32°F290276269263257249242233223
28°F340330322314307299291282270
24°F365365365359351344338332320
20°F365365365365365365365364349
16°F365365365365365365365365365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
98% of years
24°F or colder
66% of years
20°F or colder
20% of years
16°F or colder
3% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
2,676
Cooling degree days, base 65°F
1,474
Growing degree days, base 40°F
7,939
Growing degree days, base 45°F
6,201
Growing degree days, base 50°F
4,667
Growing degree days, base 55°F
3,382
Growing degree days, base 60°F
2,329

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January584017
February413062
March3381153
April19618277
May67121520
June11261701
July0406871
August0361826
September6243687
October10661421
November3791111
December575021

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 5.3 km from Durham. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00041715 (Chico Univ Farm). Public domain.